Rotary drum drier



Oct. 16, 1951 H. J. sTlEGER ROTARY DRUM DRYER 4 Sheets-Sheet 2 Filed sept. 21, 1949 Oct. 16, 1951 4 Sheets-Sheet 3 Filed sept. 21, 1949 Oct. 16, 1951 H. J. STIEGER 2,571,778

ROTARY DRUM DRYER Filed sept. 21, 1949 4sheets-sheet 4 1- /m/enr Patented Oct. 16, 1951 UNI-TED STATES PATENT OFFICE ROTARY DRUM DRIER Helmut J olln Stieger, Brough, England Application September 21, 1949, Serial No. 116,977 In Great Britain September 8, 1948 7 claims. (ci. 15s- 10) This invention relates to the condensation and evaporation of liquids, in particular natural and artificial solutio-ns such as milk, coffee solution or other beverage. 'Y

An object of the invention is to provide apparatus for the continuous production of a condensate or powder from such liquid by such quick drying but at temperatures below the boiling point of the liquid that solids in the liquid are not appreciably affected.

A further object of the invention is to provide such apparatus in which evaporation is eifected by infra-red rays and assisted by a current of air with control of the temperature such that the boiling point of the liquid is not reached.

A still further object of the invention is to provide such apparatus with the advantages of the simplicity of the known drum drying process, which is carried out by means of steam heated cylinders, whilst obtaining a dried product equivalent to that obtained from the :large and expensive spray drying apparatus.

The above and further objects of the invention will be apparent from the following specication in which the invention is more fully described with reference to the accompanying drawings which are given for purposes of illustration and not of limitation.

In these drawings:

Figure 1 is a plan diagrammatic view of a complete liquid drying plant, utilising electrically generated infra-red rays,

Figure 2 is a sectional elevation, taken on the line II-II of Figure 1 looking in the direction of the arrows, with minor parts omitted for clarity,

Figure 3 is an end elevation of the evaporating part of the apparatus being a view on the line IIl--III of Figure 4, with part broken away to show the internal construction,

Figure 4 is a longitudinal section of the evaporator being a view on the line IV-IV of Figure 3, and

Figure 5 is a half-section of a modied form of reector in the evaporator.

Referring now to the said drawings and in particular to Figures 1 to 4 thereof, an endless moving surface in the form of a cylinder I composed of polished or plated metal, glass or glazed or ceramic coated metal, which is closed off at each end by metal end plates 2, 3 (see Figure 4) which are held in position by means of securing rods 4, is mounted for rotation about a, horizontal axis by means of hollow stub shafts 5, 6 respectively disposed centrally of and vextending through the end plates 2,k 3 towhich rthey are 2 made fast as by welding. The stub shafts 5, 6 are carried by anti-friction ball bearings 1, 8 held between metal plates 9, IIJ and II, I2 respectively of which the plates 9, II extend laterally of vertical pillars or supports I3, I4 to which they are made fast.

Extending around and spaced from the cylinder I is a reflector which focusses the rays of infra-red generators (later to be described) evenly over an area of the periphery of such cylinder. This reflector is conveniently highly polished or plated metal and is preferably formed as two arcuate parts I5, I6 as illustrated which are carried by pairs of plates I "I, I8 and I92Il respectively of which the plates I8 and 20 may engage behind the plate I2 to be located `with respect thereto by threaded studs 2I, 22 (see Figure 3) on the plate I8 entering slots 23,24 in the plate I2 and similar threaded studs 25, 26 on the plate 20 entering further slots 2l, 28 and held fast as by Wing nuts 29 on such threaded studs; the other two plates I1, I9 engaging in lik-e manner with the plate I0 in an arrangement which permits removal of the reflectors I5, I6 to expose the cylinder I for ease in cleaning after Sl-ackening the wing nuts 29.

Electrical heater elements 30 generating infra-r red rays in the form of metal covered rods of a construction known per se are arranged to extend across between the plates Il, I8 and I9, 20 in the spaces between'the cylinder I and the reflectors I5, I6 and beyond such plates I1, I8 and I9, 20 respectively such heater elements 30 terminate in terminals 3|, 32 by means of which they are connected in the electrical circuit. The projecting ends of the heater elements 30 and their terminals 3|, 32 are enclosed by arcuate strips 33, 34 and 35, 36 extending normal to the plates I'I, I8 respectively and co-operating plates 31, 38 in the case of the heater elements 30 associated with the reflector I5 of which there are, in the embodiment illustrated, sixteen. The heater elements 30 associated with the reflector I6, of which there are eight in the embodiment illustrated, are similarly protected by pairs of Varcuate plates 39, 40 and 4I, 42 normal to the plates I9, 20 and co-operating plates 43, 44. The heater elements 30 are connected in series or in parallel or some in series and others in parallel and it will be noted that the heaters 30 associated with the reflector I5 are closer together, to give greater intensity, than those associated with the reflector I6.

The reiiectors I5.,Y I6 are externally provided with heat insulating coverings 45, 46 respectively composed, for example, of asbestos Wool in order to minimize heat losses.

Substantially centrally of the reilectors I5, I6 in the spaces between them and the periphery of the cylinder I are tubes 41, 48 respectively which extend through the plates I1, I8 and I9, 20 being beyond the plates I1, I9 closed oi and beyond the plates I8, 20 extending through the pl-ates 38, 44 for connection to an evacuating pump 49 which is driven by an electric motor 50 (see Figure 1) for the purpose which is later explained in the description of the operation of the apparatus. These tubes 41, 48 are adjacent the cylinder I provided each with at least two rows of holes I respectively through which air (indicated by wavy arrows) which freely enters at the ends of the reilectors and flows over the periphery of the cylinder I, may enter due to the suction created by the pump 49.

The stub shaft 6 (see Figure 4) is at its outer end closed by a plug 52 whilst the stub shaft 5 is provided with a tubular extension 53 to form an overflow discharge into a water tank -54 (see Figure 1). A tube 55 extends through the stub shaft l5 to reach down near to the bottom of the cylinder I at the far end and water is forced through this tube 55 into the cylinder I by a pump 56 driven by an electric motor 51 and drawing water from the tank 54 through a pipe 518. The cylinder I is kept half full of water the excess of which returns to the tank 54 so that, when the pump 56 is operating there is a continuous circulation of water which is employed for regulating the temperature of the cylinder either by reduction for which purpose a coil 99 is provided in the tank 54 through which a coolant may circulate, or by increase for which latter purpose the tank 54 is also provided with electrical immersion heaters 59, 69.

The stub shaft 5 (see Figures l and 4) carries a toothed wheel 6i which meshes with an endless chain 62 which passes around an output toothed Wheel 63 of a change speed mechanism 614, oi any convenient design, receiving power from an electric motor 65 through the medium of an endless belt 66 which passes around driving and driven pulleys 61, 58 respectively. The cylinder I is thus rotated unidirectionally as indicated by the arrow in Figure 2 at a, speed determined by the setting of the change speed mechanism 64.

An open sided liquid trough 69 carried by the supports 53, I4 is positioned adjacent the periphery of the cylinder I, where it is exposed between the ends of the reflector assemblies I5, I6, such that the cylinder I forms the wall on the open side and as it rotates draws a film of liquid onto its periphery. The liquid is pumped to the trough 69 through a pipe 'It by a pump 1I which is driven by an electric motor 12. The pump 'II draws the liquid through a pipe 13 from a reservoir tank I4 and the correct level of liquid in the trough 69 is maintained by providing an overflow at an appropriate height from which a pipe 15 returns the excess liquid back to the tank 14.

Below the trough 59, a scraper blade 16 is provided to make contact with the periphery of the cylinder I to scrape oir the dried product which falls vinto a collecting bin 11 (see Figure 2).

The air drawn out by the pump 49 is discharged from the pump through a pipe 1B to a two-way valve 19 which in one position connects the pipe 'i8 to a discharge pipe 89 opening to atmosphere and in the other position connects the pipe 18 to a pipe 8l leading to a heatingcoil 82, in the liquid tank 14, which is open to atmosphere at its end 93. Thus the valve 19 may be operated either to allow the discharged air, which is hot, to escape to atmosphere or to pass to the heating coil 82 for the purpose of preheating the liquid when so desired.

The electrical circuit comprises mains 484 connected through an isolating switch 85 to a terminal block 86 from which connections are taken to the electric motor 65 through a switch 81, to the heater elements 3D through a current regulator l88 and holding relay 89, to the electric motor 51 through a switch 99, to the immersion heaters 59, 60 through switches 9|, 92 respectively, and to the electric motor 12 through a switch 93 and the electric motor 50 through a switch 94.

In the operation of the plant as for example in the drying of milk into powder, liquid or precondensed milk is lled into the reservoir tank 14 and the switch -85 closed. The switches 9|, 92 are closed to complete the circuit to the immersion heaters 59, 60 so that their heating up heats the water in the tank 54 which is then circulated through the cylinder I on closing the switch in the circuit to the motor 51. The cylinder I is set rotating on closing the switch 81 in the circuit of the motor 65. The switches 93, 94 are closed so that the pump 1I starts to pump milk into the trough 69 from the reservoir and the motor 50 works the pump 49 to draw out through the tubes 41, 48 air which freely enters at the extremities of the reflectors I5, I6 and ows through the spaces between them and the cylinder I. The relay 89 closes to complete the circuit to the heaters 30 which heat up and generate infra-red rays to an intensity controlled by varying the current supply by lthe regulator 88. The infra-red rays impinge upon, and are reilected by the reilectors I5, I6 onto, the periphery of the cylinder I which has picked up a film of milk thereon as it moves past the trough 69. The heating eiect of the infra-red rays causes the water in the milk lm to vaporize and the water vapour given 01T is carried along with the air flowing along over the cylinder I to enter the tubes 41, 48 through the holes 5I therein. This air also receives some heat from the heaters 39 so that hot air and hot water vapour pass through the pump 49 but this heat need not be wasted Vas it may be circulated through the valve 19 and pipe 8I to the heating coil 82 to pre-heat the milk in the reservoir 14. The dried lm of milk is scraped off the cylinder I by the scraper blade I6 and falls into the bin 11.

The warm cylinder I and the intensity of the infra-red rays, particularly at the start of the cycle, quickly evaporate the water in the milk without the milk reaching a temperature exceeding its boiling, as the temperature at the periphery of the cylinder I is controlled by the water circulated through the cylinder which also'has a cooling eiect as either or both immersion heaters maybe switched off when the temperature of the watery approaches a desired `upper limit and then if further reduction in temperature is necessary by circulating coolant through the coil '99. As the lower range of temperatures for infrared heaters is of the order of 400 to 600 Fand as such temperatures are in excess of the boiling point of milk and most other liquids, it might be desired to evaporate, the rays, if allowed to, would raise the temperature of the milk or 'other liquid beyond that necessary for evaporation were it not for the temperature control by the circulation of water in the cylinder I. By means. of this control the temperature during evaporation can be kept down to the order of 75 to 85 C. so avoiding a cooked milk effect with reduced solubility due to changing the solid constituents of the milk or other liquid. The temperature of operation is also regulated by varying the current supply to change the intensity of the infrared rays.

The process is continuous until the amount of milk or other liquid to be treated is nearly exhausted when the electric switches are opened and the moving parts of the plant allowed to come to rest. The plant described above is intended for reducing a liquid such as milk or other natural or articial solution for example a solution of colTee, to a dry powder but it could also be used for condensing such liquid to a reduced water content as by increasing the speed of rotation of the cylinder I or reducing the intensity of the infra-red rays or by both of these expedients.

Instead of Continuous reectors I5, I6 as described above, a number of flat strip reflectors 95 may be employed when, in a convenient construction as illustrated in Figure 5, arcuate sheets 96, 91 are shaped to have projections 98 which form channels to receive and hold the strip reliectors 95. This arrangement has additional advantage in that the projections 98 act as baffles and tend to cause the air, which ows through the spaces around the cylinder I, more to traverse close to the periphery of such cylinder` which action is assisted by providing the rows of holes 5I in the tubes 41, 48 adjacent to the periphery of the cylinder.

I claim:

1. An evaporative system'comprising a rotary drum, a relatively stationary shell concentrically and at least partially surrounding said drum and having a radical spacing therefrom, a heating means disposed partially about the periphery of said drum and within said spacing, and means including a conduit disposed in said spacing for conducting a current of air through said spacingr and in Contact with said heating means, said conduit being disposed so as to conduct air directly into said spacing from the exterior of said shell.

2. An evaporative system as set forth in claim 1, wherein said means also comprises a split sector of said shell, said split sector being exposed to atmosphere.

3. An evaporative system as set forth in claim 2, said conduit in said spacing comprising a suction tube to induce air to flow into said shell through said split casing, around a portion of said drum, and out of said spacing through said suction tube.

4. An evaporative system as set forth in claim 2, including an additional suction tube within said spacing and disposed on the opposite side of said split sector relative to said rst suction tube, whereby said tubes induce a current of air to enter said casing through said split sector causing said current of air to divide in opposite peripheral paths in passing around said drum toward said suction tubes.

5. An evaporative system comprising a rotary drum, a relatively stationary shell concentrically and partially surrounding said drum and having a radial spacing therefrom, a heating means disposed partially about the periphery of said druml and within said spacing, including means for circulating water at a predetermined temperature through said drum, including a circulatory system for said water, comprising a tank having a heating means and a cooling means therein, and respective control elements for controlling said means. y

6. An evaporative system according to claim 1, including reflector means comprising a plurality1 of flat reector strips held in channels formed by projections in a backing sheet, said projections also serving as baiiles which cause the air owing over the cylinder to tend to move closer thereto.

7. An evaporative system according to claim 1, wherein said heating means comprises a plurality of electrical infra-red generators of elongated shape disposed parallel to the axis of said drum and spaced from each other substantially about the periphery of said drum, and said shell comprises polished plates concentrically spaced from said generators to reilect the rays therefrom toward said drum.

HELMUT JOHN STIEGER.

REFERENCES CITED The following references are of record in the i'ile of this patent:

UNITED STATES PATENTS France Mar. 15, 1943 

